Polymerization of vinyl chloride with n-chlorophthalimide modifier



United States Patent POLYMERIZATION OF VINYL CHLORIDE WITH N-CHLOROPHTHALINIIDE MODIFIER Dexter C. Seymour, Wyckolf, N. 1., assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey No Drawing. Application November 26, 1952, Serial No. 322,803

4 Claims. (Cl. 260-92.8)

This invention relates to the polymerization of vinyl chloride, and more particularly to the production of polyvinyl chloride of lower molecular weight.

Polyvinyl chloride resins enjoy a reputation for toughness and durability. One of the principal difficulties in adapting these resins for many applications resides in their high softening temperature. For example, if it is desired to mill polyvinyl chloride into thin sheets the milling temperatures necessary are quite high, i. e., from 300 F. to 340 F. These high temperatures increase the difiiculties in processing the resins. culty encountered during high temperature processing of polyvinyl chloride is a tendency of the resin to decompose. Various stabilizers, e. g. zinc stearate, cadmium stearate, alkyl tin compounds, are commonly added to the polyvinyl chloride to prevent thermal decomposition, but

these compounds are effective in retarding decomposition for only a limited time at the temperatures employed. Another undesirable characteristic of polyvinyl chloride resins is their low solubility in readily available solvents. These disadvantages may be overcome by producing polyvinyl chloride of lower molecular weight.

I have discovered that when vinyl chloride is polymerized in the presence of a small amount of N-chlorophthalimide, the molecular weight of the resultant polyvinyl chloride is lower than in polymerization without the N-chlorophthalimide. The N-chlorophthalimide acts as a molecular weight modifier or regulator, and the molecular weight of the resultant polyvinyl chloride is lower, the higher the amount of N-chlorophthalimide employed. Further, the average molecular weight of the polymer remains essentially constant over the whole course of the polymerization. Thus, a polyvinyl chloride of any desired average molecular weight and with uniform properties may be prepared simply by adjusting the amount of regulator added to the vinyl chloride reaction mixture.

The range of N-chlorophthalimide used in the present invention may be from 0.1 to 8% based on the vinyl chloride monomer depending on the molecular weight of the polyvinyl chloride desired. Generally not more than 6% of N-chlorophthalimide will be used. All parts and percentages referred to herein are by weight.

The N-chlorophthalimide may be used as a molecular weight regulator for vinyl chloride in the various conventional methods of polymerization, viz. bulk or mass or so-called oil-phase polymerization of the liquefied vinyl chloride; solution polymerization where the vinyl chloride is dissolved in a solvent; suspension or bead or granular polymerization where the vinyl chloride is suspended in the form of large droplets and agitated in an aqueous medium generally containing a nonemulsifying suspending agent such as protein or gum; and emulsion polymerization where the vinyl chloride is emulsified in water by means of a surface-active emulsifying agent. Details of these methods of polymerization generally are found in Unit Processes in Organic Synthesis by P. H. Groggins, Third Edition, pages 847-858 (published by McGraw A further difliall) Hill Book Company, Inc., New York, 1947), and details of the methods of polymerization specifically directed to vinyl chloride are found in Vinyl and Related Polymers by C. E. Schildknecht, pages 392-398 (published by John Wiley & Sons, Inc., New York, 1952). The regulator of the present invention, as suggested above, is preferably added to the monomer charge before initiation of polymerization in order to obtain the most uniform properties in the polyvinyl chloride product of the polymerization, but, if desired, the vinyl chloride polymerization may be initiated and partially carried out in the absence of the regulator to give a conventional high molecular weight to the polymer thus formed in the first part of the polymerization, and thereafter the regulator may be added to the partially polymerized reaction mixture to give a lower molecular weight to that portion of the polyvinyl chloride formed later in the presence of the regulator of the present invention.

The polymerization reaction is carried out at 25 C. to 60 C. in the presence of a conventional free radical type polymerization initiator, such as a peroxygen or azo catalyst. Examples of peroxygen catalysts are inorganic per oxides, e. g. hydrogen peroxide and persalts, such as alkali persulfates, alkali perborates, alkali percarbonates; and organic peroxides, e. g. diacetyl peroxide, dibenzoyl peroxide, acetyl benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, tertiary butyl hydroperoxide. Examples of azo catalysts are alpha, alpha,-azobisisobutyronitrile, and p-methoxybenzene diazo thio-2-naphthyl ether. Catalytic amounts from 0.05% to 2% based on the vinyl chloride monomer may be used.

In the following examples which illustrate the invention, differences in molecular weight of various vinyl chloride polymers are shown by differences in the intrinsic viscosities of the polymers, the lower the molecular weight, the lower will be the intrinsic viscosity. The intrinsic viscosities in the examples were obtained from viscosity measurements at 30 C. of cyclohexanone solutions of the vinyl chloride polymers and of the cyclohexanone solvent. The intrinsic viscosity [1;] is defined by the equation:

lim 1]=c 0 C Z) where 71 1 is relative viscosity (i. e. viscosity of the solution of polymer relative to that of the solvent), and c is concentration of polymer in grams per cc., the concentration selected being such that 1 has a value of from 1.15 to 1.4. Intrinsic viscositymay also be defined by the equation:

lim [n]=- where 1 is specific viscosity, and 1 =1 1, and 7 and c are as in the formula first above.

EXAMPLE I Into each of a series of five pressure tubes was weighed 0.53 g. of alpha, alpha-azobisisobutyronitrile. The tubes were cooled to Dry Ice temperature (77 C.) and into each of four of them was placed 0.3 g. of N-chlorophthalimide (1.5% of the Weight of vinyl chloride to be taken). The fifth tube served as a control. The tubes were then sealed to the vacuum line, the pressure therein was lowered to less than 10' mm., and 19.9 g. of liquid vinyl chloride was distilled into each. After being frozen in liquid nitrogen, the tubes were sealed off and each tube was heated at 30 C. for a different length of time so as to get a different extent of conversion of monomer to polymer from tube to tube.

After the heating step the unreacted vinyl chloride in each tube was measured and the conversion of monomer to polymer was calculated. The polymer in each tube was then isolated and washed several times with methanol, and its intrinsic viscosity measure. The data are summarized in Table I:

The intrinsic viscosities in Table I clearly show that those polymers prepared in the presence of N-chlorophthalimide have a much lower intrinsic viscosity than the control and accordingly a loWer molecular weight. Moreover, the constancy of the viscosity of the N- chlorophthalimide-containing polymers, regardless of the extent of conversion, illustrates that, for a given ratio of regulator to monomer, the polymer molecular weight is substantially independent of the extent of conversion to which the reaction is carried.

In view of the many changes and modifications that may be made Without departing from the principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection afforded the invention.

1. The method which comprises polymerizing vinyl chloride at 25 C. to 60 C. in the presence of a free radical producing polymerization initiator and 0.1% to 8% of N-chlorophthalimide based on the weight of the vinyl chloride monomer.

2. The method which comprises polymerizing vinyl chloride in an aqueous medium at 25 C. to 60 C. in the presence of a free radical producing polymerization initiator and 0.1% to 8% of N-chlorophthalimide based on the weight of the vinyl chloride monomer.

3. A process for production of polyvinyl chloride latex which comprises polymerizing vinyl chloride in aqueous emulsion at 25 C. to 60 C. in the presence of a free radical producing polymerization initiator and 0.1% to 8% of N-chloroph-thalirnide based on the weight of the vinyl chloride monomer.

4. A process for production of granular polyvinyl chloride which comprises polymerizing vinyl chloride in non-emulsified aqueous suspension at 25 C. to 60 C. in the presence of a free radical producing polymerization initiator and 0.1% to 8% of N-ehlorophthalirnide based on the weight of the vinyl chloride monomer.

References Cited in the file of this patent UNITED STATES PATENTS 2,533,525 Snyder Dec. 12, 1950 

1. THE METHOD WHIC COMPRISES POLYMERIZING VINYL CHLORIDE AT 25*C. TO 60*C. IN THE PRESENCE OF A FREE RADICAL PRODUCING POLYMERIZATION INITIATOR AND 0.1% TO 8% OF N-CHLOROPHTHALIMIDE BASED ON THE WEIGHT OF THE VINYL CHLORIDE MONOMER. 